1) Field of the Invention
The present invention relates to medical devices and, in particular, to a multi-layered device for treating a target site within the body, such as a vascular abnormality.
2) Description of Related Art
Medical devices such as occluders, flow restrictors, shunts, and stent/grafts are known in the art. For example, devices may be made with a single layer of braided wire fabric to occlude, restrict, or shunt flow through vessels, organs, cavities, or the like. These single-layered devices may be elongated to a reduced diameter for delivery through a catheter and resume their memorized shape when released from the delivery catheter.
Medical devices, such as multi-layered occluders and stent grafts, have also been developed in order to occlude or exclude vascular abnormalities. For example, the medical devices may include multiple layers of coaxially disposed layers of material that are configured to substantially slow the flow of blood and facilitate thrombosis. The idea is that having a greater metallic surface area using a multi-layered device speeds clot formation in comparison to single layer devices and eliminates the need for an additional material such as a polyester fabric often included in single layer devices. If the layers of material are tied together, the layers must elongate the same to be able to be tied at the middle of their longitudinal axis and to be grasped at their ends for loading within a delivery system. If the layers do not elongate the same, one of the layers will be longer than the others in a drawn down configuration, such that some of the layers will be difficult to grasp for delivery. When the layers have the same elongation, the braid geometry is similar between the layers, which can create holes in the device when the layers line up the same. Altering the braid geometry may prevent these gaps, but may lead to differences in elongation, as described above.
Multi-layer devices may be lower in delivery profile than single metal layer devices which incorporate an additional polyester fabric to facilitate occlusion because the metal filaments in a multi-layer device use smaller diameter wire and the multiple layers can all be reduced substantially in diameter together by elongation, where as the polyester fabric must be folded over itself for delivery, causing greater delivery profile in single layer devices. The profile for delivery of multiple layer devices is determined by the additive thickness of each layer in the elongated state. It would be advantageous, if all the benefits of a multi-layer device could be achieved with a lower delivery profile such as by delivering each layer sequentially. A lower delivery profile would provide for a smaller sized delivery catheter, a smaller puncture size into the vasculature, and less trauma to the vascular tissue in passage of the delivery catheter through the vasculature. In addition, smaller catheters are more flexible, and the device may be able to be placed in more difficult to reach anatomical sites such as through smaller diameter vessels or through more tortuous pathways.
Therefore, there is a need for a medical device that is capable of effectively treating various target sites within the body. Moreover, there is a need for a medical device that may be easily delivered and adequately anchored at the target site. In addition, there is a need for a medical device that may be delivered to a target site that is less traumatic to the vasculature and that may be used to prophylactically treat various conditions that may be in more difficult to reach anatomy.